Environmental Engineering Reference
In-Depth Information
60
Madrid gray clay
50
40
30
20
10
0
10
6
0.1
1
10
100
1000
10,000
100,000
Matric suction (
u
a
-
u
w
), kPa
Figure 12.31
SWCC for Madrid grey clay in terms of volumetric water content versus soil
suction (after Escario and Juca, 1989).
Table 12.6 Soil Parameters for Estimating the Shear
Strength Equations for Madrid Grey Clay
practice. However, it should also be remembered that
laboratory equipment is available for the measurement of
unsaturated soil shear strength properties. The geotechnical
engineer should insist on performing laboratory shear
strength tests in cases where the expenditure is warranted.
In summary, the shear strength equation by Oberg and
Sallfors (1997) appears to capture the general pattern of
shear strength variation with suction but may over estimate
the shear strength of unsaturated soils. The equations by Goh
et al. (2010) and D.G. Fredlund et al. (1996) appear to give
reasonable estimations of shear strength, particularly in the
intermediate- to high-suction range. These equations appear
to estimate the peak shear strength in a reasonable man-
ner for the intermediate soil suction range. The predictions
of shear strength when using the Vanapalli et al. (1996b)
equation are somewhat sensitive to the selection of residual
suction. It can be difficult to accurately determine residual
suction on the logarithmic scale of soil suction.
Equations
Additional Parameters
Oberg and Sallfors (1997) SWCC, S
D.G. Fredlund et al.
(1996)
κ
=
2
.
69,
θ
s
=
0
.
507, SWCC
Vanapalli et al. (1996b)
θ
s
=
0
.
507
,θ
r
=
0
.
108, SWCC
Goh et al. (2010)
n
d
=
0
.
55,
ψ
aev
=
110 kPa,
PI, SWCC
presented illustrate the level of confidence that can be
anticipated when using estimation procedures for the shear
strength of unsaturated soils. It appears that the proposed
estimation equations will serve as an adequate tool for
assessing the unsaturated soil shear strength in engineering
120
D. G. Fredlund et al. (1996)
100
80
Goh et al. (2010)
60
40
Oberg and Sallfors (1997)
20
Vanapalli et al. (1996b)
0
0
50
100
150
200
250
300
Matric suction (
u
a
-
u
w
), kPa
Figure 12.32
Comparison of estimations of shear strength from various proposed equations and
direct shear strength measurements on Madrid grey clay (after Escario and Juca, 1989).
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